The invention relates to a method and an apparatus for use in light emitting diode segments forming numeric displays such that the individual segment display area is many times that of the diode itself and is particularly useful when the display area is to be a long, narrow rectangle. This invention is of particular applicability to diodes having an approximately Lambertian light emission pattern, where most of the emitted light is in a cone with a half angle of 45.degree. around the normal to the diode.
Segmented light emitting diode displays are well known, especially in the familiar seven segment variety that is used in numerical displays. A problem in these segments is that the area of each segment is many times the area of the light emitting diode and where the segment is a long thin rectangle, there is a lack of uniformity to the light given off by the segment. Since the diode chips are normally mounted in the geometric center of the segment there is a "hot spot" or a brighter than average illumination in the region of the segment directly over the diode which detracts from the effectiveness and readability of the display. Light emitting diodes with a Lambertian emission pattern give off most of their light in a cone with a 45.degree. half angle with an axis normal to the diode which accentuates and compounds the hot spot problem.
In the past the general method of reducing "hot spots" was to add a large amount of scattering media to the translucent plastic between the diode and the segment surface. This would diffuse the light emitted by the diode such that there would be a uniformly luminous output but at the cost of a greatly diminished output intensity. The scattering of the light results in a 3 to 6% loss in energy each time the diode emitted light is refracted or reflected. If enough scattering material is placed in the translucent medium to achieve a uniform appearance in the segment, the overall light output is diminished considerably and vice versa, if the amount of scattering material is reduced to increase the brightness, the uniformity is impaired thus degrading the quality of the segment.